Add basic docs for JavaScriptCompiler override API

lib/handlebars/compiler/javascript-compiler.js

@@ -29,23 +29,23 @@ JavaScriptCompiler.prototype = {
     return [revision, versions];
   },
 
-  appendToBuffer: function(string, location, explicit) {
-    // Force a string as this simplifies the merge logic.
-    if (!isArray(string)) {
-      string = [string];
+  appendToBuffer: function(source, location, explicit) {
+    // Force a source as this simplifies the merge logic.
+    if (!isArray(source)) {
+      source = [source];
     }
-    string = this.source.wrap(string, location);
+    source = this.source.wrap(source, location);
 
     if (this.environment.isSimple) {
-      return ['return ', string, ';'];
+      return ['return ', source, ';'];
     } else if (explicit) {
       // This is a case where the buffer operation occurs as a child of another
       // construct, generally braces. We have to explicitly output these buffer
       // operations to ensure that the emitted code goes in the correct location.
-      return ['buffer += ', string, ';'];
+      return ['buffer += ', source, ';'];
     } else {
-      string.appendToBuffer = true;
-      return string;
+      source.appendToBuffer = true;
+      return source;
     }
   },